Drawing furnace



Jan. 28, 1936. LE ROY A. LINDBERG DRAWING FURNACE Filed Jan. 14, 1935 2Sheets-Sheet 1 Jy/emara2? Jan. 28, 1936. LE ROY A. LINDBERG 2,029,175

DRAWING FURNACE Filed Jan. 14, 1935 2 Sheets-Sheet 2 J mr,

Patented Jan. 28, 1936 DRAWING FURNACE Le Roy A. Hndberg, Evanston,111., assignor to Lindberg Engineering Company, Chicago, 111., a

corporation of Illinois Application January 14, 1935, Serial No. 1,753

2 Claims.

My present invention relates to a drawing or tempering furnace. Thespecial improvements herein disclosed are such as to supply the chargeunder treatment with highly heated air which is maintained atsubstantially uniform temperature at every point in the furnace. This isaccomplished in part by heating the furnace through convection only. Thepresent improvements are directed also to the arrangement and locationof the several operating units, each with respect to the others, so asto promote accessibility, safety, and eiflciency in service. With afurnace so constructed and operated, distinctly superior results areattainable.

These and other objects 01' my invention may be realized from aconstruction as shown in the accompanying drawings wherein Figure 1 is acentral vertical section through the furnace in its entirety;

Fig. 2 is a horizontal section therethrough on line 2-2 of Fig. l; and

Fig. 3 is an enlarged detail in section on line 3-3 of Fi 1.

So far as concerns my present invention, the furnace may be of any ofthe usual types-muffie, well, etc. By way of example, a well type offurnace is illustrated. As shown, it utilizes in its constructioncertain walls which define a well W open at the top but adapted to beclosed by a lid L which may be moved to and from position with the aidof an elevating hook 5 and a swinging bracket 8. When in the closedposition indicated in Fig. 1, the well is substantially sealed againstthe outside atmosphere. The well constitutes the chamber in which thecharge is heat-treated.

To one side of the well and separated therefrom by a wall I!) is aheating chamber E. This chamber extends vertically adjacent the well toone side thereof for substantially its entire length. The wall I llterminates short of the chamber bottom so as to leave a communicatingopening of ample size. A duct l5 extends from this opening inwardly andupwardly within the heating chamber to connect with a housing 18 whereinmay be mounted a tan ll 0! the blower type. The discharge opening 28 ofthe housing lies adjacent a partition 2| extending horizontally acrossthe heating chamber above the blower. The fan shaft, as shown, isjournaled in bearings 22 carried exteriorly upon removable panels 23forming part of spaced walls 24 between which the heating chamber islocated. By removing these panels the entire unit may be taken out intoa pit alongside of the well, whenever required. Connection with a powersource may be conveniently established by a belt running from a pulley29 on the fan shaft.

Mounted within the heating chamber preferably by suspension, ls aheating unit U which desirably comprises interconnected resistance coilsadapted to be heated through connection with a source of electricalenergy. This heating unit, as shown, comprises a head 25 below which thecoils are supported and above which is a cap plate 26 of enlarged sizeor diameter adapted to rest upon a shelf 21. Electrical connectionsdisposed on the upper side of the cap plate may be protected by a cage28, as shown. It will be observed that the heating unit is veryaccessible and may easily be removed, whether hot or cold, to bereplaced by another similar unit, the entire operation requiring perhapsnot more than two minutes time.

At a point in the upper region of the heating chamber, preferably justabove the heating unit therein, is a distributing passageway 30extending circumferentially around the well. Numerous ports 3| establishcommunication between this passageway and the interior of the well. Thearrangement is such that the heated air1 is supplied directly to acharge within the we i.

The charge to be treated may be placed in a pot P of a size and shape tofit within the well. Desirably the walls of the pot and its bottom areforaminous to promote the direct circulation of heated air therethrough.When introduced into the well the pot may be rested upon a series ofblocks 35 by which the bottom of the pot is supported in an elevatedposition above the opening to the duct l5. Accordingly, there ismaintained throughout the well and heating chamber an uninterruptedpassageway through which air may be circulated and recirculated inresponse to operation of the blower. The direction of circulationpreferably, but not necessarily, is laterally from the heating unit,thence downwardly through the charge chamber, and then upwardly throughthe heating chamber. As will be explained later, the circulation maypossibly be reversed and still produce satisfactory results.

In practice, the air of maximum temperature is that which freshly leavesthe heating unit. Passing into the annular distributing chamber, it thenenters the well at the top to be immediately drawn downwardly throughthe charge in the pot. On its way to the bottom of the well the air iscooled somewhat as the result of interchange of heat units. The airwhich then is relatively cool and dense enters the blower, and is againadvanced to the heating unit to be reheated and recirculated as before.The conduction of heat to the charge is direct and is accomplished byconvection. The walls surrounding the charge impart little or no heatthrough radiation.

Two important features of this invention are (1) the speed of aircirculation and (2) the remote location of the heating unit. The blowertype of fan which is recommended may be operated at a speed of say 3600R. P. M. to circulate air at a high rate of speed. With air circulationof such rapidity, there is substantially no temperature change duringtravel through the circuit, once the air is heated to a workingtemperature. It may accordingly be feasible to circulate the air ineither direction although, in theory at least, it is preferable that theair should proceed downwardly through the charge chamber. The blowertype of fan is suggested as it works better against a back pressure andexerts a positive propelling force which results in greater circulatingcapacity.

There is a distinct advantage in having the heating unit locatedremotely with respect to the charge chamber. The chamber for each may beconstructed with special reference to the temperatures it must s and,and insulation between these chambers will serve as mutual protection.Higher temperatures may, with safety to the charge, be employed in suchan arrangement. The dangers of overheating, excessive temperaturefluctuations, etc., in the charge chamber are greatly reduced by havingthe heating unit remotely located. And the heating unit itself is betterprotected against damage resulting from mishandling of the charge as itis moved into or out of the furnace.

As already suggested, the present improvements may be embodied invarious types of furnaces, and the foregoing description of a well typeis by way of example only. The entire construction might be above groundas well as below. Of importance is (l) the employment of a heating unitwhich is removed from the charge; (2) the removability of the heatingunit independent of everything else; (3) the independent removability ofthe blower; and (4) the circulation of air at a temperature and speedwhich will insure controlled direct and uniform heating of the charge.

I claim:

1. In a drawing furnace having a charge chamber open at the top togetherwith a removable cover therefor. the combination of walls defining aseparate heating chamber extending vertically adjacent the chargechamber and in free communication therewith adjacent its bottom, meansproviding a horizontal distributing passage circumferentially of thecharge chamber in its upper region and in communication with the upperregion of the heating chamber, a heating unit mounted within the heatingchamber, and means below the heating unit for drawing air from thebottom region of the charge chamber, sending the air upwardly past theheating unit to be thereby raised in temperature, and then circulatingthe heated air through the distributing passage for downward dischargeinto the charge chamber.

2. In a drawing furnace, the combination of walls defining a chargechamber and, insulated therefrom, a, heating chamber in adjacentrelation with spaced communicating passages therebetween, means withinthe heating chamber for positively circulating air directly through bothchambers. a heating unit within the heating chamber for heating the airso circulated, a mounting for the circulating means such that the lattermay be removed through one wall of the heating chamber withoutdisturbing the circulating means, and a mounting for the heating unitpermi'ting the latter to be removed directly from the heating chamberwithout disturbance of the circulating means.

LE ROY A. LINDBERG.

